Scratch the stilt wheels

Rutan's white knight has to have a ground clearence greater than
the height of the rocket it carries and take off requires greater
thrust than climbing to altitude. This looks like a job for a
specialized catapult. Elevated tracks on two bridge structures,
perhaps a mile long. Even a parallel stage could be accomidated. The
aircraft could land conventionally or perhaps be guided to and caught
by the same carriages that accelerated it.